Cu 2p Photoelectron and 2p 3/2-Valence-Valence Auger Electron Spectra of Cuprate Superconductors

Abstract

We have observed many-body effects in both the Cu 2p photoelectron and 2p3/2-valence-valence (L3VV) Auger electron spectra for thin films of Bi2Sr2Cax Cu1+x O6+2x (x=0, 1, 2), La2-x Srx CuO4 (x=0, 0.13), and ErBa2Cu3O7-x ,y (x<y). We reviewed the relationship between the many-body effects and high-T c superconductivity of cuprate superconductors. Enlargements of both intensity ratio and energy separation of the |cd10L> to |cd9> lines in the 2p spectra corresponded with an increase of the mixing of |d8L> and |d7> states in the L3VV spectra. Enlargement of the parameters of many-body effects resulted from an increase in covalency of the Cu–O bond. An enlargement of the transfer integral is required for realization of high-T c superconductivity of Bi–Sr–Ca–Cu–O and La–Sr–Cu–O systems. The 90 K superconductivity in Er–Ba–Cu–O and Y–Ba–Cu–O systems was realized by increasing the charge transfer energy.